a. Field of the Invention
The present invention relates generally to orthotic devices for use in shoes, and, more particularly, to a construction for forming an ultra-thin orthotic device which occupies a minimum amount of volume within the interior of a shoe.
b. Background Art
Orthotic devices are typically contoured, plate-like structures which fit in a shoe so as to correct/control the position and function of the foot. Since the most critical functions of the foot generally involve the heel and midfoot portions, a degree of rigidity is required in these areas in order for the device to carry out its biomechanical purposes. Hence, many devices of this type have a rigid, resiliently flexible plate or cap which extends from the heel of the foot through the midfoot, to the area generally beneath the metatarsal heads, sometimes referred to as the "ball" of the foot. Forward of this point, in the area extending beneath the toes, it is advantageous for the device to be more flexible and cushioning in nature.
Consequently, the rearfoot plate is often formed of a generally rigid material such as fiberglass, graphite fiber-resin composites, various types of plastics, or combinations of these or similar materials, for example, while the forefoot portion (often referred to as a forefoot "extension") is typically formed of a layer of soft, cushioning material such as dense foam rubber or the like. The rearfoot and forefoot pieces are ordinarily bonded to the bottom of a top cover which ties the two together.
While such prior devices can be extremely effective in terms of their function, they present several difficulties from the standpoint of efficient manufacture. Firstly, while the top cover usually does not serve a critical function in terms of controlling the motions of the foot, it is nevertheless required in order to join the two other components together and adds significantly to the material cost of the product.
Also, it is critical that a strong bond be formed between the top cover and the underlying pieces to ensure that these do not come apart during extended use, and this is quite difficult and expensive to achieve in practice. For example, only certain, specialized adhesives are able to form an effective bond between the top cover (which is typically formed of Naugahide.TM. or a layer of similar material) and the rubber/fiberglass of the lower layers, and such adhesives are both expensive and difficult to work with. Moreover, even when using proper adhesives, the surfaces of the components must be roughened in order to ensure a proper bond: In practice, this means that the mating surfaces of the pieces, particularly the top surface of the fiberglass/plastic plate, must be roughened with a grinder or sander before application of the adhesive, and this is a laborious and time-consuming process which adds greatly to the expense of the product. The layer of adhesive also adds to the overall thickness of the device.
The need to include a top cover also presents a problem from the standpoint that this often makes the device too thick for use in many types of shoes. This has been a longstanding problem, particularly in the area of women's high-heeled shoes (although it would be understood that the advantages of the present invention are not limited to that particular application). The interior volume of high-heeled shoes (and some other types of shoes) is extremely limited, and hence there is very little extra space available to accommodate the thickness of an orthotic device. This is in part due to stylistic considerations, which tend to dictate that such shoes be as small and light in appearance as possible, but there are important functional reasons as well: Since the foot is immobilized in a high-heeled shoe and does not function in a normal manner (i.e., it does not go through the normal phases of the gait cycle, from heel strike to toe-off, in the same manner as it would if the person was wearing an ordinary shoe or walking barefoot), it is critical that the keel counter at the rear of the shoe fit very tightly around the person's heel. This stabilizes the foot/shoe and also keeps the heel from pulling out of the shoe as the foot moves towards toe-off, however this also means that there is almost no additional depth available in the heel area to accommodate an orthotic device.
Because of the need to include a top cover with a reasonable degree of durability, it has heretofore been virtually impossible to produce a practical orthotic device having a thickness less than about 3-4 millimeters. This is simply too thick for such devices to be used in most types of high-heeled shoes, and a number of prior attempts have been made to get around this problem by eliminating material from the shoe liner or from the heel area of the device itself; none of these approaches has been entirely satisfactory, due in part to the additional work which is required and/or the decrease in strength this causes.
Yet another difficulty with the construction used in such prior devices is that the attachment of the forefoot cushion or extension in fixed relationship to the rigid rearfoot plate means that there can be no lengthwise adjustment of the components, so that separate sizes of device must be produced and stocked for each size of shoe/foot. Naturally, this adds considerably to the manufacturer's overhead for the product, as well as adding to the expense and difficulty for a practitioner or retailer to maintain a complete stock of the devices.
Accordingly, there exists the need for a form of construction for an orthotic insert which eliminates the need for a top cover or similar separate connecting layer to join the rigid rearfoot and flexible forefoot portions of the device. Furthermore, there exists a need for such a construction which produces an orthotic insert having minimal thickness and which requires a minimum of volume within the interior of the shoe. Still further, there exists a need or such an insert which can be assembled quickly and efficiently, without requiring special adhesives or labor-intensive preparation techniques. Still further there exists a need for such an insert which allows for lengthwise adjustment between the rearfoot plate and forefoot extension, so as to permit a single device to be adjusted to fit more than one size of foot/shoe.